alt Hacker NewsWell yes, that's what UB means. It's a singularity, you run into it and there's no longer a specified requirement for the behavior that will follow.
Rust also has UB, btw, https://doc.rust-lang.org/reference/behavior-considered-unde..., so I don't know where it is that people have imagined this is something the C and C++ language designers went out of their way to foist upon you.
If you want to write code for a VAX, then you can use the K&R C compiler where it had defined outcomes for everything. If you want to write portable C code for modern CPUs then it's fair to ask what the C language standard is supposed to define for each of those CPUs and OSes and ABIs.
And a bunch of people were nice enough to do that for you and I, but because they are not deities, there are things that they had to leave out to make the language useful, so they did.
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> I don't know where it is that people have imagined this is something the C and C++ language designers went out of their way to foist upon you.
They did. Most other languages, the vast majority of which are also memory safe languages, go out of their way to do the opposite, and give meaning even to erroneous programs. Some things slip through the cracks, and generally language designers and implementers work hard to get rid of UB.
C/C++ is the only ecosystem that has fully embraced UB as a way of life. They are the only compilers that make full use of "UB is bad and cannot ever happen" as a core tenet in how optimizations are designed. Rust UB is at least a little different. Rust UB can only be the result of unsafe code and is meant to be limited in blast radius, and is absolutely not meant as a loophole for compilers to just do whatever to make the code faster.
C/C++ have a surprisingly large set of UB, too. Thankfully, the rest of the software world is rising up and the committees are starting to make things like gasp signed arithmetic overflow into defined behavior.
But don't hold your breath.
> Rust also has UB, btw
Not at all the same. C and C++ are full of hazards and I get the impression it’s genuinely difficult to avoid entirely in normal code bases, and typically impossible to avoid statically. Whereas in Rust it’s all gated behind the unsafe keyword, and if you don’t use it (and most code bases never need to use it), you cannot encounter UB; and that scoping makes it far easier to control and handle correctly.